Phosphors are a class of materials that absorb incident electrical or electromagnetic energy and reradiate electromagnetic energy. The output electromagnetic radiation of the phosphor is usually in the visible range of the electromagnetic spectrum, although phosphors that reradiate in the infrared or ultra-violet range can also be produced. A critical manufacturing step for increasing the performance characteristics of phosphor materials, is that the phosphor must be annealed at high temperatures prior to use. Most phosphor materials require an annealing temperature of at least 900.degree. C.
In industries such as semiconductor manufacturing, rapid thermal annealing (RTA) or rapid thermal processing (RTP) technology is widely used to anneal. To anneal silicon wafers, the wafers are positioned under flashlamps and heated to temperatures of 1250.degree. C., in time frames of less than ninety seconds. In such an application, the silicon wafer is rapidly heated to about 900.degree. C.-1100.degree. C., and soaked at that temperature. Finally the heat source is removed and the silicon wafer is allowed to return to room temperature. Silicon has a melting point of 1410.degree. C.; as such the silicon wafer never reaches its melting point as it is annealed.
Similarly, RTP has been used to anneal zinc sulfide based electroluminescent phosphors deposited on high temperature glass substrates. Zinc sulfide electroluminescent phosphors will anneal at temperatures of approximately 550.degree. C. As such, a glass substrate having a stress relief point at 625.degree. C. is used. Again, the annealing temperature is held well below the stress relief point of the phosphor substrate, and the melting point of the glass substrate is not exceeded during the annealing process.
When certain phosphors, such as cathodoluminescent (CRT) phosphors, are applied to low temperature substrates, such as fiber optic windows, manufacturing problems occur. In such applications the annealing point of the cathodoluminescent phosphor is well above the melting point of the substrate. Cathodoluminescent phosphors have an annealing temperature that is well above the temperature at which the fiber optics and other low temperature glasses plasticize. When annealing cathodoluminescent phosphors on such low temperature glasses, the temperature of the substrate glass cannot be elevated to the phosphor annealing temperature without being damaged. In such an application, RTA and RTP manufacturing techniques necessitate a compromise in either the annealing of the phosphor, the integrity of the substrate, or both, since both the phosphor and the substrate cannot be conventionally heated to the needed annealing temperature.
It is therefore a primary object of the present invention method to anneal phosphor materials when applied to substrates having melting points below the annealing temperature of the phosphor without compromising the annealing of the phosphor or the integrity of the substrate.